There are various known water pumps. For example, JPH08-100652A (FIG. 3) describes a water pump which includes a drive shaft (38) serving as a drive side rotation body for operating an auxiliary, a driven side rotation body (36) arranged coaxially with and connected to the drive shaft for integrally rotating, and a pump impeller (37) which integrally rotates with the driven side rotation body. According to the construction of the foregoing water pump, the drive shaft and the driven side rotation body are coaxially connected at the shaft center by means of a dog and cam joint or bolt-nut fastening, and the power from the drive shaft is transmitted to the impeller.
A water pump described in JP2004-52723A (FIG. 1) includes driven side rotation bodies (18, 25) which are arranged in parallel with an output shaft of an engine serving as a drive side rotation body, and a pump impeller 30 which integrally rotates with the driven side rotation body. With the construction of the foregoing water pump, the output shaft of the engine and the driven side rotation body are connected by means of a belt to transmit the power from the output shaft.
Because the water pump described in JPH08-100652A is positioned inside a crankcase, the water pump cannot have a visual check. Further, because the driven side rotation body is coaxially and directly connected to the drive shaft at the center of the shaft, high accuracy is required for an alignment of the drive shaft and the driven side rotation body, which increases manufacturing cost in order to maintain the precision. Still further, because the auxiliary, a connecting portion (e.g., a joint), and the water pump are aligned along an axial direction, the space necessary to be ensured for positioning the auxiliary the connecting portion and the water pump in the axial direction is increased.
Particularly, when the drive side rotation body and the driven side rotation body are connected by means of a dog and cam joint and when the joint is made of rigid material (e.g., metal), noise may be generated by metal-to metal contact of the joint.
On the other hand, the water pump described in JP2004-52723 requires ensuring the space for manageability of the belt exclusive for activating the water pump. Further, an outer shape of a pulley serving as the driven side rotation body is required to have highly precise roundness in order to smoothly transmit the rotation, and the manufacturing cost is increased in order to ensure the accuracy. Further, because load from the belt is directly applied to the water pump, parts (e.g., a pulley, a body, and a bearing) are required to have adequate strength and durability.
A need thus exists for an impeller apparatus for a water pump and a water pump, which rotates an impeller by transmitting rotation of the drive side rotation body which operates an auxiliary to the driven side rotation body.